Generally, front ferrules and back ferrules are used in the connection of pipes or tubes. FIG. 5 is a sectional view showing a pipe connector using conventional ferrules.
As shown in the drawing, the pipe connector using the ferrules includes a connector body 1, a drive nut 4, and a front ferrule 2 and a back ferrule 3 that are interposed between the connector body 1 and the drive nut 4. The pipe connector compresses and clamps the outer circumferential surface of a pipe 5.
In detail, when the drive nut 4 is threaded over the connector body 1 and thus moved forward, the front ferrule 2 and the back ferrule 3 that are disposed between the inner circumferential surface of the drive nut 4 and the outer circumferential surface of the pipe 5 are pushed and moved forward. During this process, front ends of the front and back ferrules 2 and 3 are changed in shape and embedded into the outer circumferential surface of the pipe 5 so that the pipe connection can become more reliable.
Different kinds of pipe connectors or tube fitting structures using such ferrules and ferrule structures have been introduced. Representative examples have been proposed in Korean Patent Registration No. 10-0871624, entitled “Ferrule having relief part for reducing abrasion”, Korean Patent Registration No. 10-0803687, entitled “Ferrule having relief part for reducing abrasion”, Korean Patent Registration No. 10-0803685, entitled “Ferrule having relief part for reducing abrasion”, Korean Patent Registration No. 10-0871625, entitled “Ferrule having relief part for reducing abrasion”, Korean Patent Registration No. 10-0914946, entitled “Ferrule having relief part for reducing abrasion”, Korean Patent Registration No. 10-0987333, entitled “Tube fitting structure”, Korean Patent Registration No. 10-0987334, entitled “Tube fitting structure capable of checking degree of tightening”, and Korean Patent Registration No. 10-1196433, entitled “Tube fitting structure”.
In Korean Patent Registration Nos. 10-0871624, 10-0803687, 10-0803685, 10-0871625 and 10-0914946, at least one concave part is formed in the inner circumferential surface of the back ferrule so that partial load, abrasion or torque applied to the pipe and the pipe connector by the drive nut can be markedly reduced or removed.
The above-mentioned registered patents are characterized and advantageous in that some of the external axial force applied to the back ferrule is dispersed in the radial direction, whereby the ferrule and the pipe can be prevented from being undesirably deformed.
However, in the above-mentioned registered patents, after the ferrules have been changed in shape to clamp the pipe, it is difficult for the ferrules to appropriately cope with a change in external environment such as temperature, pressure or external force applied thereto. Specially, the conventional ferrules do not have any compensation function for thermal expansion or contraction of the pipe made of metal, the connector body, the drive nut or the ferrules themselves.